简介

OGNL是一种表达式语言，用于获取对象的属性或者调用方法。它在Mybatis/Struts（以及漏洞）等涉及到模版的场景中经常使用。语法这里就不讲了，需要注意的是

• OGNL大部分场景是取属性，不建议new对象
• OGNL不支持类似Groovy的safe-null，比如user?.role?.name这样的问号表达式，而SpingEL是支持的
• OGNL定位是XML中的胶水，调试方便程度肯定不如Java，因此尽可能不折腾

在Mybatis中封装了如下的OGNL，测试用例如下

Object a = OgnlCache.getValue("a + 1", Collections.singletonMap("a", 10));
System.out.println("a = " + a);//返回 11

只要在OgnlCache.getValue中打上了断点，所有的动态SQL生成过程均可以看见细节

模板替换

package com.homejim.mybatis;


import com.homejim.myabtis.GenericTokenParser;
import com.homejim.myabtis.TokenHandler;
import org.junit.Ignore;
import org.junit.Test;

import java.util.HashMap;
import java.util.Map;

import static org.junit.Assert.assertEquals;

public class GenericTokenParserTest {

  public static class VariableTokenHandler implements TokenHandler {
    private Map<String, String> variables;

    public VariableTokenHandler(Map<String, String> variables) {
      this.variables = variables;
    }

    @Override
    public String handleToken(String content) {
      return variables.get(content);
    }
  }

  @Test
  public void simpleTest() {
    GenericTokenParser parser = new GenericTokenParser("${", "}", new VariableTokenHandler(new HashMap<String, String>() {
      {
        put("driver", "com.mysql.jdbc.Driver");
        put("url", "jdbc:mysql://localhost:3306/mybatis");
        put("username", "root");
        put("password", "aaabbb");

      }
    }));

    // 测试单个解析
    assertEquals("com.mysql.jdbc.Driver", parser.parse("${driver}"));
    // 多个一起测试
    assertEquals("驱动=com.mysql.jdbc.Driver，地址=jdbc:mysql://localhost:3306/mybatis，用户名=root",
            parser.parse("驱动=${driver}，地址=${url}，用户名=${username}"));
  }
  @Test
  public void shouldDemonstrateGenericTokenReplacement() {
    GenericTokenParser parser = new GenericTokenParser("${", "}", new VariableTokenHandler(new HashMap<String, String>() {
      {
        put("first_name", "James");
        put("initial", "T");
        put("last_name", "Kirk");
        put("var{with}brace", "Hiya");
        put("", "");
      }
    }));

    assertEquals("James T Kirk reporting.", parser.parse("${first_name} ${initial} ${last_name} reporting."));
    assertEquals("Hello captain James T Kirk", parser.parse("Hello captain ${first_name} ${initial} ${last_name}"));
    assertEquals("James T Kirk", parser.parse("${first_name} ${initial} ${last_name}"));
    assertEquals("JamesTKirk", parser.parse("${first_name}${initial}${last_name}"));
    assertEquals("{}JamesTKirk", parser.parse("{}${first_name}${initial}${last_name}"));
    assertEquals("}JamesTKirk", parser.parse("}${first_name}${initial}${last_name}"));

    assertEquals("}James{{T}}Kirk", parser.parse("}${first_name}{{${initial}}}${last_name}"));
    assertEquals("}James}T{Kirk", parser.parse("}${first_name}}${initial}{${last_name}"));
    assertEquals("}James}T{Kirk", parser.parse("}${first_name}}${initial}{${last_name}"));
    assertEquals("}James}T{Kirk{{}}", parser.parse("}${first_name}}${initial}{${last_name}{{}}"));
    assertEquals("}James}T{Kirk{{}}", parser.parse("}${first_name}}${initial}{${last_name}{{}}${}"));

    assertEquals("{$$something}JamesTKirk", parser.parse("{$$something}${first_name}${initial}${last_name}"));
    assertEquals("${", parser.parse("${"));
    assertEquals("${\\}", parser.parse("${\\}"));
    assertEquals("Hiya", parser.parse("${var{with\\}brace}"));
    assertEquals("", parser.parse("${}"));
    assertEquals("}", parser.parse("}"));
    assertEquals("Hello ${ this is a test.", parser.parse("Hello ${ this is a test."));
    assertEquals("Hello } this is a test.", parser.parse("Hello } this is a test."));
    assertEquals("Hello } ${ this is a test.", parser.parse("Hello } ${ this is a test."));
  }
  @Test
  public void shallNotInterpolateSkippedVaiables() {
    GenericTokenParser parser = new GenericTokenParser("${", "}", new VariableTokenHandler(new HashMap<String, String>()));

    assertEquals("${skipped} variable", parser.parse("\\${skipped} variable"));
    assertEquals("This is a ${skipped} variable", parser.parse("This is a \\${skipped} variable"));
    assertEquals("null ${skipped} variable", parser.parse("${skipped} \\${skipped} variable"));
    assertEquals("The null is ${skipped} variable", parser.parse("The ${skipped} is \\${skipped} variable"));
  }

  @Ignore("Because it randomly fails on Travis CI. It could be useful during development.")
  @Test(timeout = 1000)
  public void shouldParseFastOnJdk7u6() {
    // issue #760
    GenericTokenParser parser = new GenericTokenParser("${", "}", new VariableTokenHandler(new HashMap<String, String>() {
      {
        put("first_name", "James");
        put("initial", "T");
        put("last_name", "Kirk");
        put("", "");
      }
    }));

    StringBuilder input = new StringBuilder();
    for (int i = 0; i < 10000; i++) {
      input.append("${first_name} ${initial} ${last_name} reporting. ");
    }
    StringBuilder expected = new StringBuilder();
    for (int i = 0; i < 10000; i++) {
      expected.append("James T Kirk reporting. ");
    }
    assertEquals(expected.toString(), parser.parse(input.toString()));
  }

}

参考

• https://miao1007.github.io/gitbook/mybatis/dynamic-sql/ognl.html